The present invention relates to multiaxially oriented high performance laminates fabricated from substantially uniaxially oriented sheets of thermotropic liquid crystal polymers.
It has in the past been very difficult to provide multiaxially oriented sheets of thermotropic polymers. When polymers which exhibit anisotropic properties in the melt phase (i.e., thermotropic liquid crystal polymers) are extruded through a slit die and drawn in the melt phase, films or sheets which exhibit high machine direction properties are obtained. However, such films or sheets also possess poor transverse directional properties which may limit the usefulness of such films or sheets in certain structural applications. It is therefore desirable to provide a sheet or film comprised of a thermotropic liquid crystal polymer which exhibits desirable multidirectional properties.
It has been suggested that films which exhibit a high degree of biaxial orientation could be prepared from nematogenic polymers by the lamination of uniaxially oriented films. See Krigbaum, W. R., et al., "Aromatic Polyamides Forming Cholesteric Phases", Journal of Polymer Science:Polymer Letters Edition, Vol. 17, pages 601-607, 1979.
It is also known to those skilled in the art that the heat treatment of shaped articles of liquid crystal polymers increases the melting temperature, molecular weight and mechanical properties of the polymer. See, for example, U.S. Pat. Nos. 3,975,487; 4,183,895; and 4,247,514.